64 GMC cant shift into 3RD

I have a 1964 GMC which has been steadily being repaired and maintained.
The latest problem has been with the transmission. It will not shift from 2nd into 3rd.
or into 3rd from neutral. Had just gotten the new shocks put on.so my budget for this year is blown. any chance this is an easy fix?

With the engine off and in Neutral,  see if it shifts into 3rd,  if not,  take the rod off the 2nd and 3rd lever at the trans and see if you can  shift the trans with your hand,,,,,,,,,we are looking to see if the problem is in the shifter or in the trans,,,,,,,

worked with it this weekend, moving the shiftier, making sure every thing was not binding.
got it into third while not running from neutral. felt it click into place like its supposed to.
and seems to be working fine now, at least around the block. will need to make sure there is not something binding.

here is more talk about shifting,,,,,,,,

https://vintage-vans.forumotion.com/t49509-difficulty-shifting-from-1st-to-2nd